Is K18 As Great As Everyone Says? Here’s My Take

If you put a bunch of beauty editors in a room, it won't be very long before the conversation turns to the products we're lusting over. One hair mask in particular has really whipped up interest across the board — so much so that most of my conversations this week with beauty-obsessed colleagues have revolved around it: K18 Leave-In Molecular Repair Hair Mask.
K18 is still fairly new, but it's already an if-you-know-you-know brand name among hairstylists, colorists, and celebrities, like Hailey Bieber. The leave-in treatment even won an Allure Best of Beauty Award in 2022. Refinery29's Beauty Director Sara Tan is a big fan, and I've heard it compared to Olaplex (one beauty editor even said it's better). TikTokers are sold, too, with the hashtag #K18 gaining an impressive 415.6 million views. So what's in this seemingly magic hair potion? And is it really that special?
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Similar to Olaplex (whose star ingredient is bis-aminopropyl diglycol dimaleate), this hair mask has a patented ingredient: the K18 peptide. Peptides are made out of amino acids which help stitch broken hair bonds back together.
Hair bonds can break easily — when you use bleach or hot tools — and the broken bonds can make hair feel dry and tangled. Just like Olaplex (my favorite is No.8 Bond Intense Moisture Mask, which takes parched hair and making it glossy), K18 has gained devotees everywhere for its ability to breath life back into hair that's a little worse for wear.
Mine really is worse for wear. Last year I had it bleached and dyed blue. When my roots began to grow out, I decided that I'd get the blue stripped out and my hair dyed back to brown. Reversing the color didn't undo the damage — far from it. Put simply, my hair is in dire need of some TLC. I've got a roster of great shampoos, conditioners, and styling products, but every now and again my lengths scream out for a surge of moisture in the form of a mask or leave-in treatment.
I know I'm not alone. Lots of us have switched up our hair color, or are at least thinking about it, with shades like candlelit brunette taking hold of hair salons everywhere. With K18 touted as the ultimate companion for dyed hair — actually, all hair — I had to give it a go.
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The product comes in two sizes and it's on the pricier side — the mini is $29 and full-size is $75 — though I am reassured that a tiny bit goes a very long way. Here's how to use it: Simply shampoo and rinse like normal but skip the conditioner. Once you're done, give your hair a squeeze to get rid of any excess water (you can towel-dry it if you like), and pull a small dollop of K18 through your hair from root to tip. After four minutes you can follow up with your styling products and dry and style your hair like you usually would.
As my hair is so brittle I was wary of the skip conditioner guidance, so I reached for my most moisturizing shampoo: Amika The Kure Bond Repair Shampoo. I rinsed and towel-dried my hair like normal (I always use an Aquis microfiber towel, which I believe is gentler on fragile strands) and raked a pump and a half of the K18 mask through my thick hair from root to tip. After just over four minutes I followed with a hair product I love right now, ARKIVE The Good Habit Hybrid Oil, and rough-dried on medium heat.
My hair from behind before K18 Leave-In Molecular Repair Hair Mask
My hair from behind after K18 Leave-In Molecular Repair Hair Mask
I'll bring you the positives first. My hair felt instantly thicker and a lot stronger. The volume was long-lasting, even after styling. I could tell that my strands were so much more resilient during straightening and I wasn't terrified that my hair would totally snap off, thanks to the bleach. There aren't any negatives per se, but I really expected this to work miracles and it fell short in terms of feel. I expect a lot from my hair products and one of my main requirements is silky, glossy hair. While this did exactly what it says on the bottle and fortified my fragile strands well, my hair wasn't particularly soft or frizz-free, which was disappointing.
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So how does it fare compared to other hair conditioners and glossing waters, like Elvive Dream Lengths Wonder Water and salon-favorite Kérastase Chroma Absolu Soin Acide Chroma Gloss? When it comes to texture and finish, I have to admit that I prefer both of these — particularly Wonder Water, which is a fraction of the price of K18. Chroma especially helps to patch over broken and split strands temporarily. If you're an R29 regular, you'll know that I'm a huge Olaplex No.8 stan, too. Unlike K18 you have to rinse it out, but it delivers both softness and strength.
I'd probably reach for K18 when my hair is in need of a cut and my split ends are at their worst. It's pretty much the hair equivalent of scaffolding and props up limp, fragile strands brilliantly. But if you're looking for shine above all else, the products I mentioned above are the ones I'll be keeping in rotation this year.
This story was originally published on Refinery29UK.
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